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Mudstone on east beach of Lyme Regis, England East Beach 1 2006.JPG
Mudstone on east beach of Lyme Regis, England

Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from shale by its lack of fissility (parallel layering). [1] [2]


The term mudstone is also used to describe carbonate rocks (limestone or dolomite) that are composed predominantly of carbonate mud. [3] However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals. [2]

The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene. [4]


There is not a single definition of mudstone that has gained general acceptance, [5] though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than 0.063 millimetres (0.0025 in). [6] Individual grains this size are too small to be distinguished without a microscope, which means that most classifications emphasize texture rather than mineral composition, [5] and mudstones have historically received less attention from petrologists than have sandstones. [7] The simplest definition is that a mudstone is a fine-grained clastic sedimentary rock that is not laminated or fissile. [5] Most definitions also include a requirement that the rock contain significant amounts of both silt- and clay-sized grains. One common requirement is that a mudstone is a mudrock (a rock containing more than 50% silt- to clay-sized particles) in which between a third and two-thirds of the mud (silt and clay) fraction is clay particles. [7] [8] Another definition is that mudstone is a sedimentary rock in which neither silt, clay, nor coarser grains is predominant. [9] Rock of this composition that does show laminations or fissility is sometimes described as mudshale rather than mudstone. [8]

The lack of fissility or layering in mudstone may be due to either original texture or the disruption of layering by burrowing organisms in the sediment prior to lithification. Mudstone looks like hardened clay and, depending upon the circumstances under which it was formed, it may show cracks or fissures, like a sun-baked clay deposit. [1]

When the mineral composition of mudstones has been determined, using such techniques as scanning electron microscopy, electron probe microanalysis, or X-ray diffraction analysis, they have been found to be composed primarily of clay minerals, quartz, and feldspars, with a variety of accessory minerals. [10]

Carbonate mudstone

A Mudstone: few small components in a micritic matrix, width of picture is 32 mm DunhamMudstone.jpg
A Mudstone: few small components in a micritic matrix, width of picture is 32 mm

In the Dunham classification (Dunham, 1962 [11] ) system of limestones, a mudstone is defined as a mud-supported carbonate rock that contains less than 10% grains. Most recently, this definition has been clarified as a matrix-supported carbonate-dominated rock composed of more than 90% carbonate mud (<63 μm) component. [3]

The identification of carbonate mudstone

Thin section photomicrograph of carbonate mudstone 14 x2 PPL.jpg
Thin section photomicrograph of carbonate mudstone

A recent study by Lokier and Al Junaibi (2016) [3] has highlighted that the most common problems encountered when describing a mudstone is to incorrectly estimate the volume of 'grains' in the sample - in consequence, misidentifying mudstone as wackestone and vice versa. The original Dunham classification (1962) [11] defined the matrix as clay and fine-silt size sediment <20 μm in diameter. This definition was redefined by Embry & Klovan (1971 [12] ) to a grain size of less than or equal to 30 μm. Wright (1992 [13] ) proposed a further increase to the upper limit for the matrix size in order to bring it into line with the upper limit for silt (63 μm).

Mudstone mineralogy on Mars

Curiosity rover - mudstone mineralogy - 2013 to 2016 on Mars (CheMin; December 13, 2016)
NOTE: JK for "John Klein", CB for "Cumberland". CH for "Confidence Hills", MJ for "Mojave", TP for "Telegraph Peak", BK for "Buckskin", OD for "Oudam", MB for "Marimba", QL for "Quela", and SB for Sebina. (For locations/drillings, see image) PIA21146-MarsCuriosityRover-MudstoneMineralogy-20161213.png
Curiosity rover - mudstone mineralogy - 2013 to 2016 on Mars (CheMin; December 13, 2016)
NOTE: JK for "John Klein", CB for "Cumberland". CH for "Confidence Hills", MJ for "Mojave", TP for "Telegraph Peak", BK for "Buckskin", OD for "Oudam", MB for "Marimba", QL for "Quela", and SB for Sebina. (For locations/drillings, see image)

On December 13, 2016, NASA reported further evidence supporting habitability on the planet Mars as the Curiosity rover climbed higher, studying younger layers, on Mount Sharp. [15] Also reported, the very soluble element boron was detected for the first time on Mars. [15] In June 2018, NASA reported that Curiosity had detected kerogen and other complex organic compounds from mudstone rocks approximately 3.5 billion years old. [4] [16] [17] [18] [19] [20] [21] [22]

See also

Related Research Articles

<span class="mw-page-title-main">Limestone</span> Type of sedimentary rock

Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.

<span class="mw-page-title-main">Shale</span> Fine-grained, clastic sedimentary rock

Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness. This property is called fissility. Shale is the most common sedimentary rock.

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and cementation of particles

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation, transport, deposition and diagenesis. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures.

<span class="mw-page-title-main">Kerogen</span> Solid organic matter in sedimentary rocks

Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 1016 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold.

<span class="mw-page-title-main">Siltstone</span> Sedimentary rock which has a grain size in the silt range

Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.

<span class="mw-page-title-main">Conglomerate (geology)</span> Sedimentary rock composed of smaller rock fragments

Conglomerate is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts. A conglomerate typically contains a matrix of finer-grained sediments, such as sand, silt, or clay, which fills the interstices between the clasts. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay.

<span class="mw-page-title-main">Mudrock</span> Type of sedimentary rock

Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than 116 mm and are too small to study readily in the field. At first sight, the rock types appear quite similar; however, there are important differences in composition and nomenclature.

<span class="mw-page-title-main">Dunham classification</span>

The Dunham classification system for carbonate sedimentary rocks was originally devised by Robert J. Dunham in 1962, and subsequently modified by Embry and Klovan in 1971 to include coarse-grained limestones and sediments that had been organically bound at the time of deposition. The modified Dunham Classification has subsequently become the most widely employed system for the classification of carbonate sedimentary rocks with 89% of workers currently adopting this system over the alternative Folk classification scheme

<span class="mw-page-title-main">Clastic rock</span> Sedimentary rocks made of mineral or rock fragments

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks, and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic to refer to sedimentary rocks and particles in sediment transport, whether in suspension or as bed load, and in sediment deposits.

<span class="mw-page-title-main">Mars general circulation model</span>

The Mars general circulation model (MGCM) is the result of a research project by NASA to understand the nature of the general circulation of the atmosphere of Mars, how that circulation is driven and how it affects the climate of Mars in the long term.

<span class="mw-page-title-main">Wackestone</span> Mud-supported carbonate rock that contains greater than 10% grains

Under the Dunham classification system of limestones, a wackestone is defined as a mud-supported carbonate rock that contains greater than 10% grains. Most recently, this definition has been clarified as a carbonate-dominated rock in which the carbonate mud component supports a fabric comprising 10% or more very fine-sand grade or larger grains but where less than 10% of the rock is formed of grains larger than sand grade .

<span class="mw-page-title-main">Gale (crater)</span> Martian crater

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<span class="mw-page-title-main">Grainstone</span> Type of limestone

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<span class="mw-page-title-main">Aeolis quadrangle</span> One of a series of 30 quadrangle maps of Mars

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<span class="mw-page-title-main">Yellowknife Bay, Mars</span>

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